Telethermometer receiver and display device

ABSTRACT

A device for receiving a signal having a frequency which is a linear function of a temperature being monitored at a remote location and for providing a display of that temperature value is disclosed. The display digits are energized in accordance with the values stored in respective ones of a plurality of concatenated decade counters which in turn periodically receive their count by gating into them, for a prescribed length of time, a reshaped demodulated signal which is in turn derived from the received signal. This demodulated signal is mixed with a predetermined frequency from a signal source the frequency of which corresponds to 0* Fahrenheit. Decision means for providing a sign indication for positive or negative temperatures is also disclosed.

United States Patent [191 Deebel et al.

[ Oct. 16, 1973 [54] TELETHERMOMETER RECEIVER AND 2,900,601 8/1959 Corl et a1 324/79 D DISPLAY DEVICE 3,304,504 2/1967 l-lorlander 235/1513 [75] Inventors: g gigf fi gfik f gggz j Primary Examiner-John W. Caldwell Morris bot'h of 1 W a ne of Assistant Examiner-Robert J. Mooney Ind y Attorney-Richard T. Seeger et al.

[73] Assignee: The Magnavox Company, Fort Wayne [57] ABSTRACT A device for receiving a signal having a frequency [22] Flled' 1972 which is a linear function of a temperature being mon- [21] Appl. No.: 244,081 itored at a remote location and for providing a display of that temperature value is disclosed. The display dig- [52] U S C] 340/181 340/206 324/79 D its are energized in accordance with the values stored 328/41 235/92 in respective ones of a plurality of concatenated de- [511 Int Cl G08c 19/16 cade counters which in turn periodically receive their [58] Fieid 206 count by gating into them, for a prescribed length of 235/92 4/79 D time, a reshaped demodulated signal which is in turn 329/11 1 derived from the received signal. This demodulated signal is mixed with a predetermined frequency from a l 56] References Cited signal source the frequency of which corresponds to 0 Fahrenheit. Decision means for providing a sign indi- UNITED STATES PATENTS cation for positive or negative temperatures is also dis- 3,2l7,l44 11/1965 l-linnah 324/78 D l ed 3,244,983 4/1966 Ertman 324/79 D 3,071,725 H1963 Mcwaid 328/ 141 20 Claims, 9 Drawing Figures 37 65 67 INCDMING SCHMITT AN D B B $|GNAL(A TFUGGER 1 GATE 1 2 COUNTER l l 69 1 SEC. GATE RESET I 2 f (D) f '7) RESET; l r l l r t SCHMWT +|o D IO +10 MIXER FILTER T AND DECADE DECADE DEcADE DECADE R166 2 FGATE 2 COUNTER COUNTER COUNTER COUNTER A T 4| SEC. GATE r57 [59 6| BCD To 7 BCD To 7 BCD To 7 4096 HERTZ SEGMENT SEGMENT SEGMENT OSC'LWOR DECODER DECODER DECODER PUSH TO RESET OBTAIN 1 H-: g' i g SEC-GATE O R 1 sEG. GATE HUNDRED DIGIT PMENIED UN 16 I975 SHEET 6 0F 7 mm H W lm TELETI'I'ERMOMETER RECEIVER AND DISPLAY DEVICE CROSS REFERENCE TO RELATED APPLICATIONS BACKGROUND OF THE INVENTION This invention relates to a telemetry receiver and more particularly to such a receiver for decoding and displaying temperature information about specified ones of several items moving through a processing line. Such information may be encoded and transmitted, for example, in accordance with the principles of the aforementioned copending application.

It is an object of the present invention to provide an economical telethermometer receiver for receiving and displaying temperature information associated with a product passing through a heating or cooling process.

It is another object of the present invention to provide a unique scheme for converting and displaying temperatures encoded as the frequency of a transmitted signal.

Yet another object of the present invention is to pro- I vide a highly accurate decoding and display telethermometerreceiver for use with one or more telethermometer transmitters.

A further object of the present invention is to provide a decoder for frequency encoded telemetry information.

A still further object of the present invention is to provide a device for decoding and displaying information about a physical parameter being monitored at a remote location.

SUMMARY OF THE INVENTION The foregoing, as well as other objects and advantages of the present invention, are achieved by providing a device fo receiving a signal the frequency of which is a substantially linear function of a physical parameter such as temperature being monitored at a remote location and for providing one or more outputs indicative of the values of one or more such physical parameters. The received frequency modulated signal is combined with a predetermined frequency signal to provide a resultant intermediate frequency signal, which contains both the sum and difference of the frequency of the two combined signals, and by passing this intermediate frequency signal through a filter and a Schmitt trigger and gating the Schmitt trigger output into a series of concatenated decade counters for a precise time interval, the count ultimately stored in the several decade counters may be displayed. The incoming signal is supplied to a second Schmitt trigger circuit, the output of which is similarly gated for a prescribed time interval into a binary counter to determine whether the incoming frequency is indicative of positive or negative temperatures.

In its preferred form the signal to be decoded by the present invention has a frequency which is a linear function of the temperature or other physical parameter being monitored. In this linear function the constant term is an integral power of two, and the incoming signal is gated into a binarycounter for one second to determine whether the number of cycles exceeds or is less than this constant term and thus to determine and display the proper sign associated with the temperature. A local oscillator having an output in cycles per second numerically equal to this constant term is combined with the incoming signal, and the difference, which now has a frequency which is a multiple of the temperature beingv sensed, is properly shaped and gated into a series of decade counters to display the magnitude of the temperature.

It is therefore still another object of the present invention to provide a linear frequency to temperature BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a view of the front panel and controls associated with the present receiving device;

FIG. 2 is a block diagram of the frequency to display converter of the present invention;

FIG. 3 is a timing diagram illustrating several waveforms associated with the circuit of FIG. 2;

FIG. 4 is a block diagram of the telethermometer receiver circuitry employed in conjunction with the receiver illustrated in FIG. 1;

FIGS. and 5b constitute a block diagram of the receiver circuitry of the present invention employing several variations on that illustrated in FIG. 4;

FIG. 6 is a timing diagram for the circuit of FIG. 5;

FIG. 7 represents the output of the audio amplifier with and without a battery alarm indication; and

FIG. 8 illustrates a printer output tape format.

DESCRIPTION OF THE PREFERRED .WEMBQQIMEHIWwW The front panel of a receiver-decoder constructed in accordance with the present invention is illustrated in FIG. 1, and the control elements are seen to include a manual selector switch 11 which, as illustrated, allows the receiver to be manually tuned to any one of six different telethermometer transmitters of a type, for example, as disclosed in the aforementioned copending application. This manual selector switch is effective only when the select mode switch 13 is in the manual position, and when the select mode switch 13 is in the automatic position the receiver sequentially tunes to each of the remote transmitters and displays its temperature information on a series of seven segment display lamps 15, 17 and 19 which are preceeded by a sign lamp 21. In the automatic mode the appropriate one of the six channel indicator lamps 23 is energized to indicate which of the six remote location temperatures is presently being displayed. The control panel contains alarm indicators in the form of a loud speaker 25 and a series of resettable visual indicators 27 to provide audible and visible indications when the parameter being monitored has exceeded some predetermined value. As

might now be expected the control panel also includes an on-off switch 29, fusing 31, a power-on indicator 33, and a switch 35 for disabling the speaker 25 at the operator's election.

A salient feature of the present invention is the manner in which the magnitude and sign of a temperature is displayed on the several display units 15, 17, 19 and 21, and these display units are similarly numbered in FIG. 2. Considering now FIG. 2 a signal received on line 37 has a frequency which is a substantially linear function of the parameter being monitored and may be represented by where K, and K are constants and desirably where K; is an integral power of 2. This incoming signal is supplied to a mixer 39 in which it is combined with a locally generated signal of a predetermined frequency from the signal source 41. Desirably the frequency in cycles per second of this locally generated signal is numerically equal to K The filter 43 is required to eliminate all frequencies except the difference frequency which may have been created in the mixing process. The filter output is supplied to a Schmitt trigger circuit 45 or similar bi-stable device such as a multi-vibrator to appropriately shape the signals which are then gated through AND gate 47 for a prescribed length of time into the lowest order or least significant digit position 49 of a plurality of cascaded decade counters 49, 51, 53 and 55. It should be noted that there are four decade counters illustrated, and only three decimal digit display devices 15, 17 and 19 which are appropriately energized by the contents of the decade counters 51, 53 and 55 by way of binary coded decimal to seven segment decoders 57, 59 and 61. Thus the number of stages in the counter is one greater than the number of decimal digit display devices, and thus the effect of the counters in conjunction with the display devices is to divide the incoming frequency by a number dependent upon the length of time that the AND gate 47 was enabled. In the present disclosed preferred embodiment this gate is enabled for a one second interval and thus the effect of ignoring the lowest order decade counter 49 is to divide by 10. If the gate were enabled for one half second, the resultant displayed value would be the signal frequency divided by twenty and in general, enabling the gate for b seconds will effectively display the numerical value of the incoming frequency divided by l/b for decade counters or a/b for modulo a counters. In other words, the actual temperature T will be displayed so long as a/b K,.

From the discussion so far it should be noted that a frequency which was cycles per second above the frequency of the locally generated signal would yield a display of 1 in the units digit position 15, and an incoming signal having a frequency 10 cycles per second less than the locally generated signal would also yield a display of one on the seven segment display lamp 15. In order to distinguish between these two possibilities the incoming signal on line 37 is also supplied to a second Schmitt trigger circuit 63 which, of course, acts as a bistable device supplying digital information to AND gate 65 which, when energized, passes this information into a binary counter 67. As noted earlier the constant term in the linear expression of frequency as a function of temperature was selected as an integral power of 2, and the locally generated signal has this same integral power of 2 as its frequency, and hence if the AND gate 65 is enabled for precisely one second the number of pulses supplied to the binary counter 67 will provide an indication of positive or negative temperature. Thus, for example, if the constant term in the linear expression is 2 4096, and the temperature is 1, the thirteenth stage in the binary counter 67, which is the highest order digit position in a 2 counter, will be in its one state, whereas if the temperature had been 1 below zero Fahrenheit this highest order binary digit position in the counter 67 would be in its zero state. The status of this highest order digit position in the counter 67 is used to energize or de-energize the vertical bar 69 in the sign lamp 21. The horizontal bar 71 is, of course, energized at all times during which the receiver is in operation.

The signal source 41 also supplies its output to a timer 73 which, through appropriate divisions and delays, provides reset signals to the counter 67 and the several decade counters 49, 51, 53 and 55 as well as enabling the AND gates 47 and 65 for a precise one second period. In one preferred embodiment the signal source 41 had a frequency of 4096 cycles per second which is 2, and by sequentially dividing this frequency by 4 then 128 and finally 8, the one second gate signal is easily derivable, thus assuring a coherent time interval.

To better understand the circuitry of FIG. 2 a hypothetical situation and some of the waveforms associated with FIG. 2 for that situation are presented in FIG. 3. If the frequency of the locally generated signal is 4096 cycles per second and if the incoming signal on line 37 is as represented by waveform (A), a signal having a frequency of 8092 cycles per second which, due to a very abrupt decrease in the parameter being monitored, drops to a signal of the frequency of 4096 cycles per second will cause the Schmitt trigger 63 to switch from one of its bi-stable states to the other as illustrated in waveform (B). If the binary counter 67 is adapted to count once for each transition of the Schmitt trigger output circuit, then this counter will count up to 8092 during a 1 second interval for the higher frequency input thus indicating a positive parameter, whereas during the lower frequency input period, as illustrated in the right half portion of the waveforms, the counter will count only to 4096 and will indicate for that count as well as all lower counts a negative parameter value. The output of the signal source 41 is illustrated in waveform (C) and this signal is subtractively combined with the waveform (A) to provide a difference waveform (D). It should be noted that the difference waveform (D) has a rather high frequency when the incoming signal is twice the predetermined frequency of the source 41, whereas when the incoming signal gets close to the same frequency as that of the signal source the frequency of the difference signal diminishes to virtually zero. The magnitude of this difference signal is not critical to the theory of operation, since it is only transitions of the trigger circuit 45 which increment the count in the several decade counter stages. This difference signal, waveform (D), is supplied to the Schmitt trigger circuit 45 which changes state in accordance with the frequency of the difference circuit and has its output represented by waveform (E). The several decade counter stages, of course, count for one second the number of transistions of this waveform E, and it should be clear from the waveform that while the frequency of the incoming signal was twice that of the reference signal, namely 8092, the decade counter stages will .accumulate a 4096 count during one second, whereas, asillustrated in the right half of FIG. 3, when the incoming signal is of substantially the same frequency as the reference signal of source 41, the Schmitt trigger circuit does not change state, and the decade counters will receive no incrementing signals thus supplying a zero indication to each of the display lamps l5, l7 and 19. In the left half of FIG. 3 the 4096 count resulting in the several decade counter stages will be displayed as 409 with, as noted earlier, a plus sign in front of itJThe six does not appear on the display elements since the decade counter 49 has no display element associated with it.

Turning now to FIG. 4, which incorporates the decoder and display circuitry of FIG. 2, an entire receiver adapted to display information from six different telemetry transmitters is illustrated. Many of the reference numerals of FIG. 4 will also be found in FIGS. 1 and 2 to designate corresponding elements, however some of the elements of .FIG. 2 have been lumped into blocks labeled with their composite functions. Incoming signals from a telemetry transmitter are received by an antenna 75 and supplied to a radio frequency amplifier section 77 which, by appropriate positioning of one section 11A of the ganged switch 11, is tuned by, for example, one crystal 79 to receive and amplify only the frequency associated with remote transmitter No. 1. Other crystals may, of course, be provided and connected to other portions of the switch 11A to tune to other transmitters. Thus the selected signal is received on antenna 75, amplified in radio frequency amplifier stage 77, and by well known techniques not illustrated converted and supplied to an intermediate frequency amplifier 81. This incoming signal may be further processed and demodulated according to well known radio receiver techniques in an audio amplifier 83 and limiter 85 and then passed to the mixer 39 and gate 65, both of which, of course, were previously discussed in referring to FIG. 2. The block representation for the gate 65 may also include as one of its inputs the Schmitt trigger 63 of FIG. 2, or the function of this Schmitt trigger may be taken over by the limiter 85. Similarly the trigger and gate 47 are illustrated as a single block 47 since in some instances the low pass filter 43 may be sufficiently sharp to eliminate the need for the trigger 45. Thus the mixer 39, signal source 41, filter 43, counter 67, and timing circuitry 73 are justas illustrated in FIG. 2, and the gates 47 and 65 are basically the same as illustrated in FIG. 2.

FIG. 4 illustrates in much greater detail the nature of the timing circuitry 73 which is enclosed within dotted lines. This timing circuitry first divides by four the frequency from the signal source 41 so as, for example, to provide a 1024 cycle per second signal which may be used as the audio source for the gated audio amplifier 87 to provide the previously noted audible alarm by way of speaker 25. This signal is further divided in its frequency by a divide by 128 counter to provide an 8 cycle per second signal which can conveniently be counted (up to four) to provide k second delays which are useful in allowing the circuitry to stabilize and providing the necessary delays so that the counts in the several registers can be returned to zero. This 8 cycle per second signal is passed through a divide by eight counter to provide 1 second enabling signals for the 6 gates 47 and 65. It should be noted that a signal on the output of the storage update unit 89returns the contents of the counters to zero, and simultaneously this signal is passed through a A second delay 91, and then,

by way of the onesecond gate 93, enables the gates and 47 to pass the one second sample into the counters, thus the counters are returned to zero-prior to the time that the gates 47 and 65 are energized. This same timing circuitry provides signals to storage update circuitry, digital to analog converter circuitry, and amplifiers for purposes of recording the periodic contents of the registers. The frequency of the incoming audio signal as present at the audio output stage also is presented to a filter which is tuned to pass frequencies corresponding to critical parameter values, and when such critical values are present the filter 95 passes a signal by way of the amplifier 97 to trigger a flip-flop 99 and simultaneously sound the audio alarm on speaker 25 and a visual indication on one of the lamps 23 of FIG. 1 to illustrate which channel and thus which transmitter has sensed a critical parameter value.

This filter 95 serves to separate the standard data from temperature data. FIG. 7 illustrates the output of the audio amplifier 83 of FIG. 4 for two conditions. Waveform (A) represents the output received from a transmitter with a depleted battery, and waveform (B) represents the data from a transmitter with a good battery. If the modulating frequency (not illustrated to scale in FIG. 7) is between 3776 and 6399 cycles per second, the data will be processed as temperature data and will be displayed on the display elements of FIG. 1. The three decimal digits representing the temperature magnitude, the proper sign indication and the degrees Fahrenheit lamp will be appropriately energized. Of course, if the frequency is less than 4,096 cycles per second the temperature will be indicated as negative, whereas if the frequency is above this figure the temperature sign indicator will indicate a positive temperature. If the audio frequency is less than 3,776 cycles per second the signal is not processed as temperature data but rather will be recognized and processed as a standard or confidence signal. As illustrated in FIG. 7 this standard data is transmitted by the transmitter for a three second interval during each 72 second interval to give the operator an indication that the system is working properly. An audio signal between 3,584 and 3,711 cycles per second will be recognized as an acceptable standard data signal, and the front panel display will show between 051 and 038, and the degrees Fahrenheit indicator will not be illuminated. If the incoming audio frequency is less than 3,776 cycles per second but not in the acceptance range of 3,584 to 3,711 cycles per second, then the equipment will recognize this as an unfavorable check and will display the appropriate numerical readout associated with the unfavorable standard frequency, but in addition one of the channel indicators 23 will be energized to indicate a fault and will remain energized until the corresponding reset button of the group 27 is pushed to extinguish the fault indication.

If the audio frequency from the amplifier 83 is greater than 6,399 cycles per second, the equipment identifies this signal as a battery depleted signal and again illuminates the corresponding channel indicator 23 associated with the channel on which such a battery depleted signal was received and in addition grounds the battery alarm circuit so that the audible alarm will be energized. Both the fault light 23 and the audio alarm may be disabled by pressing the proper reset button 27, or the audio alarm alone may be silenced by turning off the speaker switch 35.

The receiver-decoder is capable of monitoring any one of six transmitters when the switch 13 is in the manual mode by setting the manual select switch 11 to the selected channel. This causes a local oscillator to provide to an input mixer a frequency that when mixed with the radio frequency input will provide the proper intermediate frequency to the intermediate frequency amplifier 81. If more than one transmitter is in operation then up to six such transmitters may be sequentially sampled by putting the switch 13 in the automatic mode position so as to sequentially step the receiverdecoder through the several channels. Each channel is on for 72 seconds, which is the time required by the transmitter to transmit three bursts of data as illustrated in FIG. 7. One burst of data represents temperature, while another burst represents a standard or confidence check on the system, and the third burst, if present, indicates a depleted battery condition.

An noted earlier the receiver-decoder may be provided with an interface with a digital printer, for example, a six column printer using a pressure sensitive paper so as to allow the receiver-decoder to be unattended and yet provide a printed record of the process being monitored. An example of such a printed record is shown in FIG. 8 and provides a complete record of the information received by the receiver-decoder.

Column 6 serves to identify the type of data preceding the column 6 entry in a given line. An F indicates temperature data, a D indicates the month and day of the month on which the particular information was recorded, a G indicates a satisfactory standard data check and is preceded by the time of day on a 24 hour basis on which that check took place, whereas a B In column 6 similarly preceded by the time of day indicates that the standard data signal was bad. If the B is preceded by a series of sevens as illustrated in line 3, this indicates a depleted battery condition. For each channel change the printer provides a blank line so as to separate one channels data from the next. It should also be noted that since there is no synchronization between the several transmitters, the printing sequence may vary from channel to channel. Thus line 1 of FIG. 8 indicates that channel number 6 transmitted a 185 Fahrenheit signal on (line 2) April 23 and that (line 3) the battery was depleted at (line 4) 5:10 P.M. The middle block of data found on lines 6, 7 and 8 indicates channel 1 transmitted a 1 10 Fahrenheit signal on the same day, April 23, at 1 minute later at 17:11 or 5:11 P.M. and that the standard data signal was good. The last block of data transmitted one minute later from channel 2 indicates a bad standard data check at 5:12 P.M. with a temperature indication of 8 Fahrenheit again on April 23.

FIGS. 5 and 6 illustrate a functional block diagram and associated timing diagram of a slightly different implementation of the present invention and is perhaps best understood by tracing a signal through the block diagram. A frequency modulated signal is received at the antenna 75' and is passed through a conventional crystal control frequency modulated superheterodyne receiver comprising a radio frequency amplifier and mixer 103, a filter and intermediate frequency amplifier 105, an FM. detector and audio amplifier 107 and the local oscillator portion of the local oscillator and fault board 109. The output of the audio amplifier 107 is, of course, an audio signal in the range of 3,000 to 8,000 cycles per second and is of the nature illustrated in FIG. 7. Thus an audio signal of approximately 3 seconds duration is applied to the peak detector 111, which in turn provides a high level direct current output corresponding to the time during which audio is being received. The output of this peak detector 111 is illustrated as waveform (A) of FIG. 6. A timing board 113 is responsive to waveform (A) along with an 8 cycle per second signal and a 16 cycle per second signal, each of which is derived from the 4,096 cycle per second local oscillator 115 by effecting the appropriate divisions in the divider circuitry 117. The timing board 113 functions to provide a reset pulse (C), a one second gating signal (D), a storage update signal (E) and a print command signal (F) for the printer. The timing board 113 comprises a monostable multi-vibrator, which provides the reset pulse and the start pulse for a divide by 32 feedback divider chain. The feedback stops the divider prior to achieving its full count of 32 of the 8 cycle per second input so as to reset the counter at the end of the three second interval as well as provide the other necessary output signals. The reset pulse (C) is used to set all registers in the system to zero preparatory to the receipt of new data. The one second gate is used to clock data into the 2 register 119 and into the counting circuit 121 for the proper time interval. The storage update pulse is supplied to the static digital filter 123 so that the contents in the register 119 can be sampled at that time. The print command signal, of course, initiates printer operation.

Still further functions are derived from the timing board 113 to allow the receiver-decoder to operate in its automatic mode, prevent the display of erroneous information and interface the receiver-decoder with the printer. A data inhibit pulse from the automatic sequencing block 125 indicates that the channel is being changed and that the system is in its automatic mode. If the detected audio signal goes high less than 4 seconds after the channel has been changed, the data inhibit pulse prevents the timing sequence from being initiated, and the data will be ignored. This last provision is desirable in order to prevent partial data pulses from being processed and producing false displays or readouts.

The six channel lines which are inputs to the timing board 113 provide inputs to a pulse generator to produce a pulse every time a channel is changed. This pulse is supplied to an OR gate, the other input of which is the reset pulse so as to reset all registers to zero when a channel is changed. This, of course, prevents a carry-over of data from one channel to the next, which could introduce erroneous displays or printouts. The timing board 113 also provides a change channel pulse to the printer to advance the paper an extra line each time the channel is changed.

The output from the audio amplifier 107 is also supplied to a mixer 127 where the incoming audio frequency is mixed with a 4,096 cycle per second signal from the oscillator 115 to provide as an output to the low pass filter 129 the sum and difference of the input signals as well as harmonics of those sums and differences. The lowest frequency output from this mixer, which is the difference of the two input frequencies, is the desired signal, and the low pass filter 129 attenuates all of the higher frequency signals while passing this desired frequency to a Schmitt trigger circuit 131, which serves to reshape the signal making it compatible with the subsequent logic circuitry. The block 121 contains four decade counters and gating circuitry and in particular contains a NAND gate, one input of which is the output of the Schmitt trigger 131. The other input to this NAND gate is the one second gate signal from the timing board 113 causing the four decade counters to receive data for precisely one second. As noted earlier, only outputs from three of the four decade counters are utilized so as to provide a readout to three significant places. binary coded decimal output lines from the block 121 form the inputs to three binary coded decimal to seven bar decoders in the block 133 to provide the necessary code conversion for energizing the seven segment readout units on the front panel.

Yet another output line connects the audio amplifier 107 with a second Schmitt trigger circuit 135, which, like the trigger circuit 131, reshapes the audio signal to make it compatible with the subsequent digital circuitry. The output of the trigger circuit 135 is supplied to the 2" register 1 19 for precisely one second to determine whether the incoming frequency is greater than or less than 4,095 cycles per second. The last stage of the 2 register 119 changes to its one" state upon receipt of the 4,096th pulse, and this one state of the last stage causes the vertical bar of the plus-minus readout tube 21 to be energized indicating a positive temperature. This register 119 contains the numerical value of the incoming signal frequency, and the last seven stages may be used as inputs to a static digital filter 123. This digital filter 123 functions to determine if the incoming frequency was indicative of good or bad standard (confidence) data, temperature data, or if the data represented a depleted battery condition. The static digital filter 123 provides an output signal which is the same in width and time of occurrence as the storage update pulse on the particular output line from block 123 to indicate the type of data most recently received. If the incoming data was temperature data, two output lines are energized, one of which supplies the digital printer with the appropriate indication, and the other of which functions to energize the degrees Fahrenheit lamp, which may optionally be provided on the front panel adjacent to the temperature display information. A reset pulse supplied to the static digital filter 123 serves to extinguish the degrees Fahrenheit lamp when new data is being received preparatory to a new decision and display.

The last 10 stages of the binary counter 119 also provide an input to the ten bit digital to analog convertor 137 having a -10 to +10 volt output range corresponding to all zeros or all ones as its digital input and providing about .75 to +5.4 volts as a direct current output for the temperature range of -3() to +220 Fahrenheit.

The automatic sequencing block 125 changes the channel being received every 72 seconds, which is the longest time required to obtain three bursts of data from a transmitter. The 72 seconds is obtained by counting down from the 8 cycle per second input, and the pulse that functions to change channels is 4 seconds wide. Since the transmitter and receiver are not synchronized, if data happens to be being received when the change channel pulse occurs, the incoming detected audio functions to inhibit the channel change until this detected audio goes low again. A convertor 139 functions to convert the six channel lines into three lines of binary coded decimal information for use by the printer.

FIG. 5 also contains an alternating current to direct current convertor 101 as well as numerous elements which are analogous to those discussed earlier in reference to FIG. 4, and these elements, if identical, are marked with an identical reference numeral, whereas, if somewhat different but performing the same function, they are marked with a primed reference numeral. Thus, for example, fault lamps 23 and channel indicator lamps 23" are both employed in the embodiment of FIG. 5 with the lamps 23' being energized each time the corresponding I channel is sampled, whereas the lamps 23' are energized only upon the occurrence of a fault in a corresponding channel. The switch 11 of FIG. 4 was a simple rotary ganged switch, whereas the switches 11' of the embodiment of FIG. 5 are a series of channel select buttons having a lockout feature so that only one channel button can be depressed at any one time.

While the present invention has been described with respect to a specific embodiment, numerous modifications will suggest themselves to one of ordinary skill in the art, and accordingly the scope of the present invention is to be measured only by that of the appended claims.

What is claimed is:

1. A device for receiving a signal the frequency of which is a function of a physical parameter being monitored at a remote location and for providing an output indicative of the value of that physical parameter comprising:

a signal source of a predetermined frequency;

means for combining said received signal and said predetermined frequency signal to provide a resultant signal having a frequency which is the difference of the frequencies of the two combined signals;

decision means for providing a first indication if said received signal frequency exceeds said predetermined signal frequency and a second indication if said received signal frequency does not exceed said predetermined signal frequency; and

means for providing an indication of the magnitude of said resultant signal frequency.

2. The device of claim 1 wherein said decision means comprises a counter and means for gating the received signal to the counter for a prescribed length of time.

3. The device of claim 2 further comprising means for resetting said counter to an initial state prior to gating the received signal to the counter.

4. The device of claim 2 wherein said means for providing comprises a second counter and means for gating the resultant signal to the second counter for a prescribed length of time.

5. The device of claim 4 further comprising means for resetting the second counter to an initial value prior to gating the resultant signal to the second counter.

6. The device of claim 4 wherein said second counter comprises a first plurality of cascaded decade counters and said means for providing further comprises a second plurality of decimal digit display devices for providing a visual indication of the magnitude of said resultant signal frequency.

7. The device of claim 1 wherein said means for providing comprises a counter and means for gating the resultant signal to the counter for a prescribed length of time.

8. The device of claim 7 further comprising means for resetting the counter to an initial state prior to gating the resultant signal to the counter.

9. The device of claim 7 wherein said counter comprises a first plurality of cascaded decade counters and said means for providing further comprises a second plurality of decimal digit display devices for providing a visual indication of the magnitude of said resultant signal frequency.

10. The device of claim 1 wherein the received signal frequency is a substantially linear function of the physical parameter and the physical parameter being monitored is temperature, said predetermined signal having a frequency which corresponds to Fahrenheit.

11. The device of claim 1 wherein the physical parameter being monitored is temperature and the received signal frequency (f) is a substantially linear function of the temperature (T) and may be represented by where K and K are constants.

12. The device of claim 11 wherein K is of the form 2" where n is any natural number and said decision means comprises a binary counter having n 1 stages.

13. The device of claim 11 wherein said predetermined frequency is K cycles per second and said means for providing comprises; a divide by a counter, and means for gating the resultant signal to the counter for b seconds where a and b are real numbers and a/b K 14. The device of claim 13 wherein K is of the form 2" where n is any natural number and said decision means comprises a binary counter having n 1 stages.

15. The device of claim 13 where b 1, said counter comprising a first plurality of cascaded decade counters, and said means for providing further comprises a second plurality of decimal digit display devices for providing a visual indication of the magnitude of said resultant signal frequency, said first plurality exceeding said second plurality by l and there being no display device coupled to the lowest order decade counter.

16. The device of claim 15 wherein K is of the form 2" where n is any natural number and said decision means comprises a binary counter having n 1 stages.

17. A device for receiving a signal the frequency (f) of which is, at least under steady state conditions, a substantially linear function of a physical parameter (P) being monitored at a remote location and which may be represented by f X11) K2 where K and K are constants, and for providing an output indicative of the value of that physical parameter comprising:

a signal source having a frequency of K cycles per second;

means for combining the received signal and the signal from said source to provide a resultant signal having a frequency which is the difference of the frequencies of the two combined signals; and

means for providing an indication of the magnitude of said resultant signal frequency including a divide by K counter and means for gating the resultant signal to the counter for one second, said counter comprising a first plurality of cascaded decade counters, and said means for providing further comprising a second plurality of decimal digit display devices for providing a visual indication of the magnitude of said resultant signal frequency, said first plurality exceeding said second plurality by one and there being no display device coupled to the lowest order decade counter.

18. A device for receiving a signal the frequency of which is a function of a physical parameter being monitored at a remote location and for providing an output indicative of the value of that physical parameter comprising:

means for providing an intermediate frequency signal derived from said received signal;

a bi-stable device for reshaping said intermediate frequency signal;

a first plurality of cascaded decade counters and a second plurality of decimal digit display devices coupled thereto for providing a visual indication of the magnitude of the intermediate frequency signal, said first plurality exceeding said second plurality by one and there being no display device coupled to the lowest order decade counter;

gate means having timing means associated therewith for passing said intermediate frequency signal to the lowest order decade counter for a prescribed length of time; and

decision means for providing a first indication if said received signal frequency exceeds a predetermined value and a second indication if said received signal frequency does not exceed said predetermined value.

19. The device of claim 18 further comprising filter means disposed between said means for providing and said bi-stable device for preventing unwanted harmonics from triggering said bi-stable device.

20. The device of claim 17 further comprising decision means for providing a first indication if f is greater than K and a second indication if f does not exceed K 1K 

1. A device for receiving a signal the frequency of which is a function of a physical parameter being monitored at a remote location and for providing an output indicative of the value of that physical parameter comprising: a signal source of a predetermined frequency; means for combining said received signal and said predetermined frequency signal to provide a resultant signal having a frequency which is the difference of the frequencies of the two combined signals; decision means for providing a first indication if said received signal frequency exceeds said predetermined signal frequency and a second indication if said received signal frequency does not exceed said predetermined signal frequency; and means for providing an indication of the magnitude of said resultant signal frequency.
 2. The device of claim 1 wherein said decision means comprises a counter and means for gating the received signal to the counter for a prescribed length of time.
 3. The device of claim 2 further comprising means for resetting said counter to an initial state prior tO gating the received signal to the counter.
 4. The device of claim 2 wherein said means for providing comprises a second counter and means for gating the resultant signal to the second counter for a prescribed length of time.
 5. The device of claim 4 further comprising means for resetting the second counter to an initial value prior to gating the resultant signal to the second counter.
 6. The device of claim 4 wherein said second counter comprises a first plurality of cascaded decade counters and said means for providing further comprises a second plurality of decimal digit display devices for providing a visual indication of the magnitude of said resultant signal frequency.
 7. The device of claim 1 wherein said means for providing comprises a counter and means for gating the resultant signal to the counter for a prescribed length of time.
 8. The device of claim 7 further comprising means for resetting the counter to an initial state prior to gating the resultant signal to the counter.
 9. The device of claim 7 wherein said counter comprises a first plurality of cascaded decade counters and said means for providing further comprises a second plurality of decimal digit display devices for providing a visual indication of the magnitude of said resultant signal frequency.
 10. The device of claim 1 wherein the received signal frequency is a substantially linear function of the physical parameter and the physical parameter being monitored is temperature, said predetermined signal having a frequency which corresponds to 0* Fahrenheit.
 11. The device of claim 1 wherein the physical parameter being monitored is temperature and the received signal frequency (f) is a substantially linear function of the temperature (T) and may be represented by f K1T + K2 where K1 and K2 are constants.
 12. The device of claim 11 wherein K2 is of the form 2n where n is any natural number and said decision means comprises a binary counter having n + 1 stages.
 13. The device of claim 11 wherein said predetermined frequency is K2 cycles per second and said means for providing comprises; a divide by ''''a'''' counter, and means for gating the resultant signal to the counter for b seconds where a and b are real numbers and a/b K1.
 14. The device of claim 13 wherein K2 is of the form 2n where n is any natural number and said decision means comprises a binary counter having n + 1 stages.
 15. The device of claim 13 where b 1, said counter comprising a first plurality of cascaded decade counters, and said means for providing further comprises a second plurality of decimal digit display devices for providing a visual indication of the magnitude of said resultant signal frequency, said first plurality exceeding said second plurality by 1 and there being no display device coupled to the lowest order decade counter.
 16. The device of claim 15 wherein K2 is of the form 2n where n is any natural number and said decision means comprises a binary counter having n + 1 stages.
 17. A device for receiving a signal the frequency (f) of which is, at least under steady state conditions, a substantially linear function of a physical parameter (P) being monitored at a remote location and which may be represented by f K1P + K2 where K1 and K2 are constants, and for providing an output indicative of the value of that physical parameter comprising: a signal source having a frequency of K2 cycles per second; means for combining the received signal and the signal from said source to provide a resultant signal having a frequency which is the difference of the frequencies of the two combined signals; and means for proviDing an indication of the magnitude of said resultant signal frequency including a divide by K1 counter and means for gating the resultant signal to the counter for one second, said counter comprising a first plurality of cascaded decade counters, and said means for providing further comprising a second plurality of decimal digit display devices for providing a visual indication of the magnitude of said resultant signal frequency, said first plurality exceeding said second plurality by one and there being no display device coupled to the lowest order decade counter.
 18. A device for receiving a signal the frequency of which is a function of a physical parameter being monitored at a remote location and for providing an output indicative of the value of that physical parameter comprising: means for providing an intermediate frequency signal derived from said received signal; a bi-stable device for reshaping said intermediate frequency signal; a first plurality of cascaded decade counters and a second plurality of decimal digit display devices coupled thereto for providing a visual indication of the magnitude of the intermediate frequency signal, said first plurality exceeding said second plurality by one and there being no display device coupled to the lowest order decade counter; gate means having timing means associated therewith for passing said intermediate frequency signal to the lowest order decade counter for a prescribed length of time; and decision means for providing a first indication if said received signal frequency exceeds a predetermined value and a second indication if said received signal frequency does not exceed said predetermined value.
 19. The device of claim 18 further comprising filter means disposed between said means for providing and said bi-stable device for preventing unwanted harmonics from triggering said bi-stable device.
 20. The device of claim 17 further comprising decision means for providing a first indication if f is greater than K2 and a second indication if f does not exceed K2. 